Humans have the ability to recognize a space on the basis of a difference between images which are perceived by two eyes located at a certain distance from each other. A difference between corresponding points in images which are obtained from the different viewpoints of the left eye and right eye is called a parallax, and humans stereoscopically recognize the positional relationship among target objects by using a parallax as a clue. It is known that, by utilizing this theory, stereoscopic viewing can be achieved by providing means for displaying a right-eye image for a right eye and a left-eye image for a left eye, and by displaying the right-eye image and the left-eye image having a parallax. Here, a plurality of images having a parallax for stereoscopic viewing are referred to as “stereoscopic images”.
It is said that, in stereoscopic viewing, a human associates an angle formed between optical axes of both eyes corresponding to a parallax, that is, the degree of convergence, with a distance to a target object. Thus, if a right-eye image is relatively displaced to the right and a left-eye image is relatively displaced to the left so as to show images with a parallax, the viewer can perceive a displayed object at a point located behind an actual display surface. At this time, however, if the parallax is too large, for example, if the parallax is larger than the distance between the eyes of the viewer, more precisely, if the parallax is larger than the distance between pupils at the time when the viewer is viewing a point at infinity, a state which is impossible in nature will occur, and stereoscopic viewing is not achieved. Also in the short-distance side, an extreme parallax causes an unnatural positional relationship, makes the viewer extremely cross-eyed, and inhibits comfortable stereoscopic viewing. In this way, comfortable stereoscopic viewing can be achieved if the parallax of a stereoscopic image is within a certain range. However, if the absolute value of the parallax increases, images for both eyes are not fused and stereoscopic viewing is not achieved.
PTL 1 discloses a method for adjusting a parallax by displacing the display positions of left and right images to the left and right and displaying a stereoscopic image in a viewer-friendly manner, in the case of displaying a stereoscopic image having an excessively large parallax amount which makes it difficult or impossible to achieve stereoscopic viewing.
According to this method, parallax adjustment is performed by displacing the display positions of left and right images, the depth positions of all displayed objects are moved in the forward or backward direction, and thereby fusion of the displayed objects can be promoted. However, displacing the display positions of left and right images may generate, at the edges of displayed images, a region which cannot be displayed, and a part of an image region is lost. In the lost part, the left and right images are not paired, and stereoscopic viewing is not achieved. That is, a region where stereoscopic display is not achieved is generated. Furthermore, if an excessive parallax is given both on the far side and near side in the depth direction, difficulty in fusing images is not overcome even if depth positions are overall moved forward or backward.
PTL 2 discloses a display method for adjusting a parallax amount by enlarging or reducing left and right images, thereby enabling stereoscopic viewing of an entire screen. According to this method, the parallax of the entire screen can be reduced while stereoscopically viewing the entire screen, and images which are easily fused can be obtained.